1. Field of the Invention
The present invention relates to enhancements in the providing of security to areas through which access is afforded by means of a door and, particularly, to increasing the difficulty of obtaining an unauthorized key for operation of a lock installed in such a door. More specifically, this invention is directed to mechanical locking systems and, especially, to a novel lock and key which, in combination, provide access control, the lock "trapping" any other key which is employed in an attempt to defeat the lock. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of the Prior Art
Mechanical locks which employ one or more linear arrays of pin tumbler stacks are, of course, well known in the art. The pin tumbler stacks of such locks are radially displaceable, with respect to the axis of rotation of a plug or core, in response to insertion of a key in a keyway provided in the core. The pin tumbler stacks comprise at least an upper or driver pin, which is spring biased toward the axis of core rotation, and a driven or bottom pin. A properly bitted key will cause pin tumbler stack displacement which, typically, causes the interface between the axially aligned driver and bottom pins to be coincident with a shear line defined by the core outer circumference. Thus, a properly bitted key will permit the core, with the bottom pins, to rotate within a shell. Core rotation will, through the action of a cam or tailpiece connected to the core, cause operation of a latch mechanism.
Locks of the type generally discussed above are known in the art as "cylinder" locks. The most common manner of defeating a cylinder lock consists of "manufacture" of an unauthorized key. It is believed fair to state that it is not possible to ensure against defeat simply by designing an intricate keyway and/or through the use of various arrangements of pin tumbler stacks. Thus, there has been a long-standing desire for a lock which affords increased security and, particularly, a lock which will "trap" any unauthorized key, particularly a partly formed key which is being "patterned" in an attempt to defeat the lock. In addition to key trapping, a high level of security also dictates a unique combination of a lock and key, i.e., a lock system, which affords the lock manufacturer the ability to exercise key control by means of being the sole source of the key portion of the system.